Maleated high acid number high molecular weight polypropylene of low color

ABSTRACT

A novel, continuous process for the manufacture of novel higher molecular weight and higher acid numbered maleated polypropylenes with lower color at higher efficiencies involving specified ratios of polypropylene, maleic anhydride, and free radical initiator is described. The novel maleated polypropylenes have an acid number greater than 4.5, a yellowness index color of no greater than 76, and a number average molecular weight of at least 20,000. The process entails continuously forming an intimate mixture of molten polypropylene and molten maleic anhydride at one end of a reactor, continuously introducing a free radical initiator, and continuously removing high acid number high molecular weight maleated polypropylene of low color from the opposite end of the reactor.

This is a divisional of U.S. patent application Ser. No. 08/859,628filed May 20, 1997 now U.S. Pat No. 5,955,547, which is a continuationof U.S. application Ser. No. 08/296,208, filed Aug. 25, 1994, which isnow abandoned.

FIELD OF THE INVENTION

This invention relates to novel lower color, maleated polypropyleneswith higher acid numbers and higher molecular weights. This inventionalso relates to a novel polypropylene maleation process utilizing lowflow rate polypropylenes involving specified ratios of polypropylene,maleic anhydride, and free radical initiator.

BACKGROUND OF THE INVENTION

Grafting of monomers onto polyolefins is well known (see `PolymerChemistry` by M. P. Stevens, (Addison-Wesley), 1975, pp. 196-202).Maleation is a type of grafting wherein maleic anhydride is grafted ontothe backbone chain of a polymer. Maleation of polyolefins falls into atleast three subgroups: maleation of polyethylene, maleation ofpolypropylene, and maleation of copolymers of propylene and ethylene orother monomers.

Maleation of polyethylene provides higher molecular weight products witha noticeable decrease in melt index due to cross-linking, unless specialprovisions are made, (see for example `Journal of Applied PolymerScience`, 44, 1941, N. G. Gaylord et al (1992); and U.S. Pat. Nos.4,026,967; 4,028,436; 4,031,062; 4,071,494; 4,218,263; 4,315,863;4,347,341; 4,358,564; 4,376,855; 4,506,056; 4,632,962; 4,780,228;4,987,190; and 5,021,510). Maleation of polypropylene follows anopposite trend and yields lower molecular weight products with a sharpincrease in flow rate due to fragmentation during the maleation process(see for example U.S. Pat. Nos. 3,414,551; 3,480,580; 3,481,910;3,642,722; 3,862,265; 3,932,368; 4,003,874; 4,548,993; and 4,613,679).Some references in the literature fail to note the difference betweenmaleation of polyethylene and polypropylene, and claim maleation ofpolyolefins with conditions which are useful only for eitherpolyethylene or polypropylene, respectively. In general, conditionswhich maleate polypropylene are not ideal for maleation of polyethylenedue to the opposite nature of the respective maleation chemistries:fragmentation to lower molecular weights for polypropylene andcross-linking to higher molecular weights for polyethylene. This isshown in U.S. Pat. No. 4,404,312. Maleation of copolymers of propyleneand ethylene or other monomers follow the pattern of the majoritycomponent.

Maleations of polypropylene can also be further subdivided into batch orcontinuous processes. In batch processes all of the reactants andproducts are maintained in the reaction for the entire batch preparationtime. In general, batch maleation processes cannot be used competitivelyin commerce due to high cost. Batch processes are inherently moreexpensive due to startup and cleanup costs.

The maleated polypropylene's that are reported in the previousliterature can also be divided into two product types as a function ofwhether or not solvent is involved, either as a solvent during reactionor in workup of the maleated products. In U.S. Pat. Nos. 3,414,551;4,506,056; and 5,001,197 the workup of the product involved dissolvingthe maleated polypropylene product in a solvent followed byprecipitation, or washing with a solvent. This treatment removes solublecomponents and thus varies both the `apparent` molecular weight and theacid number. Processes using an extruder produce a product in whichsolvent soluble components remain. In addition, extruder processes oftenincorporate a vacuum system during the latter stages of the process toremove volatile lower molecular weight components. Thus differentcompositions are necessarily present in products produced in an extruderin contrast to those products from solvent processes or those which usea solvent in product workup.

Another subdivision of maleation of polyolefins concerns the state ofthe reaction process. Solvent processes, or processes where solvent isadded to swell the polypropylene (see U.S. Pat. No. 4,370,450), areoften carried out at lower temperatures than molten polyolefin (solventfree) processes. Such processes involve surface maleation only, withsubstantial amounts of polypropylene below the surface being maleationfree. Processes using molten polypropylene involve random maleation ofall of the polypropylene. Solvent processes are also more expensive inthat solvent recovery/purification is necessary. Solvent purification iseven more expensive if the process inherently produces volatileby-products, as in maleation. Note that if water is the `solvent`,polypropylene is not soluble and reaction must occur only on the surfaceof the polypropylene solid phase. Further, in aqueous processes maleicanhydride reacts with the water to become maleic acid. In these two waysprocesses containing water are necessarily different from non-aqueousprocesses. In a molten process no solvent or water remains at the end ofthe process to be purified or re-used. Thus a molten process would beenvironmentally `greener` and less expensive.

Present commercial maleation of low flow rate (high molecular weight)polypropylene by continuous processes, such as in an extruder, produceproducts with acid numbers well below 4. These products are used inadhesives, sealants, and coatings and as couplers and compatibilizers inpolymer blends. However, due to the low acid numbers, the adhesion andcoupling properties of these maleated polypropylenes are limited. Asnoted above, attempts to produce higher acid number polypropylene incontinuous processes yield higher colored products with much lowermolecular weight with maleic anhydride conversion efficiencies of 20-30%or lower (see for example U.S. Pat. No. 5,001,197). Attempts to producehigher acid number polyethylene in continuous processes yieldcross-linking, higher color, and gels (see for example U.S. Pat. Nos.4,612,155; 4,639,495; 4,751,270; 4,762,890; 4,857,600; and 4,927,888).The patent literature does describe continuous maleation of high flowrate (low molecular weight) polypropylene waxes to higher acid numbers.However, as noted above the molecular weights of the maleated waxes soproduced are even lower than that of the starting material due tofragmentations during maleation.

In light of the above, it would be very desirable to maleate lower flowrate polypropylenes in a continuous process to higher molecular weightsand higher acid numbers with lower colors than have been known before.It would also be very desirable to maleate these polypropylenes athigher efficiencies.

SUMMARY OF THE INVENTION

The composition according to the present invention comprises a maleatedpolypropylene having an acid number greater than 4.5, a yellowness indexcolor of no greater than 76, and a number average molecular weight of atleast 20,000.

The process for the production of high acid number high molecular weightmaleated polypropylene of low color comprises continuously forming anintimate mixture of molten polypropylene and molten maleic anhydride atone end of a reactor, continuously introducing a free radical initiatorinto said intimate mixture of molten polypropylene and molten maleicanhydride, and continuously removing high acid number high molecularweight maleated polypropylene of low color from the opposite end of saidreactor, wherein the weight ratio of polypropylene to maleic anhydrideis about 10 to 200, the molar ratio of polypropylene to free radicalinitiator is about 200 to 4,000, and the molar ratio of maleic anhydrideto peroxide is about 1 to 70, and wherein the melt flow rate of saidmolten polypropylene is preferably about 0.1 to 50 at 230° C.

DETAILED DESCRIPTION OF THE INVENTION

The applicants have unexpectedly discovered a novel continuous processto maleate low flow rate polypropylenes. The compositions so formed arenovel in that the color is lower, the acid number is higher, and themolecular weight is higher than previously known. The process is alsounique in that the efficient use of maleic anhydride is generally muchhigher than expected.

The composition according to the present invention has an acid numbergreater than about 4.5 (the method of determining acid number isillustrated in the examples). The maleated polypropylene compositionaccording to the present invention preferably has an acid number greaterthan 5, more preferably between 6 and 70, with an acid number between 9and 60 being most preferred. Generally, at the higher acid numbers theresulting maleated polypropylene exhibits higher adhesiveness to polarsubstrates and thus is more useful in combination with materials used inadhesives and sealants. Additionally, at the higher acid numbers themaleated polypropylene is useful as a compatibilizing agent or couplerwhen used in blends of dissimilar materials, including polymer blendssuch as a nylon and polypropylene blend. At higher acid numbers loweramounts of maleated polypropylene is needed for any of these purposes.However, due to practicality acid numbers generally above 70 aredifficult to produce economically. Thus, practical preferred limits onacid numbers of the maleated polypropylene are below 70.

The composition according to the present invention has a yellownessindex color no greater than 76 or about 75. The yellowness index coloranalysis is illustrated in the examples. At a yellowness index colorless than about 75, the resulting maleated polypropylene has a desirablecolor in that when blended with other materials it imparts less of anundesirable yellow tint or brown tint to the final product. Thus,yellowness index colors well below 75 are more preferred. The maleatedpolypropylene composition according to the present invention preferablyhas a yellowness index color less than about 65 or 60, more preferablyless than 50 with a yellowness index color less than 40 being mostpreferred.

The composition according to the present invention has a number averagemolecular weight of at least 20,000 which corresponds to a BrookfieldThermosel Melt Viscosity of at least about 16,000 cP at 190° C. Thisnumber average molecular weight is preferably as high as possible. Athigher number average molecular weights the resulting maleatedpolypropylene is more durable and flexible which is desired in manyapplications. Thus, the maleated polypropylene preferably has a numberaverage molecular weight greater than 25,000 and even greater than30,000. However, the maleated polypropylene generally has a numberaverage molecular weight less than 100,000 due to fragmentation thatoccurs during the process of maleating the molten polypropylene.Therefore, the maleated polypropylene generally has a number averagemolecular weight for the more preferred compositions between 25,000 and80,000 with a number average molecular weight between 30,000 and 70,000being most preferred.

The composition according to the present invention is made frompolypropylene that contains less than 20 weight percent of a comonomerand is preferably a homopolypropylene containing less than 5 weightpercent of a comonomer, more preferably less than 2 weight percent of acomonomer. At amounts of comonomer higher than 20 weight percent, andsometimes higher than 5 weight percent, the crystallinity of themaleated polypropylene is significantly reduced, and in the case ofethylene as comomomer crosslinking can occur.

The composition according to the present invention can be blended withmany other materials to serve as a compatibilizer, such as in blendswith nylon and polypropylene. This type of blend preferably containsabout 10 to 90 weight percent nylon, about 10 to 90 weight percentpolypropylene, and about 0.1 to 10 weight percent maleatedpolypropylene, more preferably about 25 to 75 weight percent nylon,about 25 to 75 weight percent polypropylene, and about 0.1 to 10 weightpercent maleated polypropylene.

Additionally, the maleated polypropylene composition of the presentinvention can be extended with many components such as wood flour, glassfibers, talc, and mica. The use of these components extend the materialreducing the final cost.

The process according to the present invention for producing the highacid number high molecular weight maleated polypropylene of low colorcomprises

(a) continuously forming an intimate mixture of molten polypropylene andmolten maleic anhydride at one end of a reactor, wherein the melt flowrate of said polypropylene is preferably about 0.1 to 50 at 230° C.,

(b) continuously introducing a free radical initiator into said intimatemixture of molten polypropylene and molten maleic anhydride to produce amaleated polypropylene, and

(c) continuously removing the maleated polypropylene product from theopposite end of said reactor,

wherein the weight ratio of polypropylene to maleic anhydride is about10 to 200, the molar ratio of polypropylene to free radical initiator isabout 200 to 4,000, and the molar ratio of maleic anhydride to freeradical initiator is about 1 to 70.

The process according to the present invention maleates a moltenpolypropylene that preferably has a melt flow rate of about 0.1 to 50 at230° C. For all practical purposes, a polypropylene with a melt flowrate below 0.1 is difficult to produce and requires significant torquein a twin screw extruder to be able to process. Whereas, a polypropylenewith a melt flow rate greater than 50 at 230° C. yields a maleatedpolypropylene product with a molecular weight that is lower than isgenerally useful according to the present invention. The melt flow rateof the polypropylene used to produce a maleated polypropylene of thepresent invention is more preferably about 0.1 to 40 @ 230° C., with amelt flow rate of about 0.1 to 20 @ 230° C. being most preferred.

The process according to the present invention uses a free radicalinitiator to initiate the grafting of the maleic anhydride onto themolten polypropylene. Any free radical source could be useful in theprocess of the present invention. However, peroxides are generally morepreferred due to availability and cost. Peroxides with short half livesi.e. less than 3 seconds at 180° C. are less desirable, since asignificantly higher amount of peroxide is needed and results in amaleated polypropylene product of poor color and higher cost. Thepreferred peroxides are alkyl peroxides, more preferably dialkylperoxides. Examples of suitable peroxides useful in the process of thepresent invention include ditertiary butyl peroxide, tertiary butylhydroperoxide, cumene hydroperoxide, p-menthane peroxide, p-menthanehydroperoxide and 2,5-dimethyl-2,5-bis-(t-butylperoxy)hexane withditertiary butyl peroxide and 2,5-bis-(t-butylperoxy)hexane being mostpreferred.

The process according to the present invention is conducted in acontinuous process. Any continuous process can be used in the practiceof the present invention. However, stirred pot reactors with powerfulstirring mechanisms or screw extruders are favored, with screw extrudersgenerally being more preferred due to the ease in operation andacceptability in manufacturing processes. Twin-screw extruders are themost preferred screw extruders due to their ease of use and efficientmixing action. Screw extruders are also more preferred in that thepolypropylene is maleated continuously with a shorter residence time inthe reaction zones. The use of a screw extruder in the process of thepresent invention aids in the production of maleated polypropylenes ofimproved color and higher molecular weight due in part to lessfragmentation of the polypropylene.

The process according to the present invention is preferably conductedat a weight ratio of polypropylene to maleic anhydride between 10 and200, more preferably between 15 and 120, even more preferably between 20and 100, with a weight ratio of polypropylene to maleic anhydride ofabout 25 to 60 being most preferred. At amounts of polypropylene/maleicanhydride below the ratio of 10 too much maleic anhydride is present andthe efficiencies are dramatically reduced. Whereas, at ratios above 200the amount of maleation in the final maleated polypropylene issignificantly lower. Such ratios simply increases the need for longerresidence time or recycle of low acid number maleated polypropylene.

The residence time of the polypropylene in the continuous reactordepends upon the pumping rate of the polypropylene and the size (volume)of the reactor. This time is generally longer than three times the halflife of the free radical initiator so that a second pass through therector is not needed to obtain sufficient maleation of thepolypropylene. In a stirred reactor the residence time generally variesfrom about 5 minutes to 1 hr, more preferably about 10 minutes to 30minutes. In a screw extruder this time generally varies from about 1 to3 minutes at RPMs of 50 to 400 for a single screw and about 0.45 to 2.5minutes with twin screws, more preferably about 1 to 2 minutes at RPMsof 150 to 300 with twin screws. As shown in the examples, at certain setamounts of reactants (within the general ratios of reactants required inthe present invention) a polypropylene of lower than desired acid numberis produced. In this instance the RPM in a screw extruder can be reducedor the residence time increased such that the acid number is increasedto be within the more desired acid number limits.

The molar ratio of polypropylene to free radical initiator used in themaleation process according to the present invention is preferably about200 to 4,000, more preferably about 210 to 3,500, with a molar ratio ofpolypropylene to free radical initiator of about 270 to 2,100 being mostpreferred. At amounts below the molar ratio of 200 the presence of highamounts of free radical initiator produces excess fragmentation of thepolypropylene resulting in a lower molecular weight polypropylene. Atamounts above the molar ratio of 4,000 the free radical initiator is atsuch a low concentration that efficient maleation is not obtainable.

The process according to the present invention is preferably conductedat a molar ratio of maleic anhydride to free radical initiator betweenabout 1 and 70, more preferably between about 2 and 60, even morepreferably between about 3 and 50, with a molar ratio of maleicanhydride to free radical initiator of about 3.5 to 15 being mostpreferred. At molar ratios below 1 the amount of free radical initiatoris significantly higher than required for the particular amount ofmaleation on the polypropylene, and thus increases fragmentation whilenot significantly increasing the acid number of the maleatedpolypropylene. For amounts such that the molar ratio of maleic anhydrideto free radical initiator is above 70, the efficiencies of the graftingof maleic anhydride onto the polypropylene is dramatically reduced andthe color of the resulting product is inferior.

The maleic anhydride useful for the present process is any commercialgrade of maleic anhydride. Those with maleic anhydride contents of95-100% are preferred in that fewer volatile by-products must be handledby the vacuum system. Molten maleic anhydride with a purity over 99% ismost preferred for the same reason, fewer volatiles are produced to behandled by the vacuum system.

The process according to the present invention is generally conducted ata temperature above the melting point of the polypropylene. Thistemperature is preferably between 160 and 220° C., more preferablybetween 180 and 210° C., with a temperature between 190 and 205° C.being most preferred. At temperatures much below 160 the viscosity ofthe molten polypropylene is too high to be efficiently pumped throughthe screw extruder. At temperatures much above 220° C. the fragmentationof the molten polypropylene dramatically increases and molecular weightdecreases.

The process according to the present invention is generally conductedsuch that a vacuum is used at or after step (c) to remove volatiles fromthe maleated polypropylene product.

The process according to the present invention is generally efficient,grafting onto polypropylene a high percent of the maleic anhydridepresent during the reaction, thus producing a maleated polypropylenewith grafted maleic anhydride at a preferred efficiency percent above35. This percent maleic anhydride incorporated into polypropylene can beup to or near 100 percent. However, this efficiency rate is generallyover about 40 and up to 93 percent, more preferably at least 49 percent.At efficiency rates below 35 percent, maleic anhydride recovery isincreased and cost per unit maleation onto the polypropylene is alsoincreased. However, efficiencies at or below 85 percent are generallyacceptable.

The following examples are intended to illustrate the present inventionbut should not be interpreted as a limitation upon the reasonable scopethereof.

EXAMPLES

Values of the acid number as shown in Table 1 are the average of atleast 4 determinations taken on samples obtained at 15 minute intervalsduring an hour of production. An acid number is defined as the number ofmilligrams of KOH which are required to neutralize one gram of sample.Acid numbers were obtained by titrating weighed samples dissolved inrefluxing xylene with methanolic potassium hydroxide usingphenolphthalein as an indicator. End points were taken when the pinkcolor of the indicator remained 10 seconds.

Color was measured as `yellowness index` according to ASTM RecommendedPractice E 308 for Spectrophotometry and Description of color in CIE1931 System.

Efficiencies, noted in Table 1 as `% maleic anhydride (MA) used`, werecalculated based on the percent of the fed MA which was incorporatedinto the product. (Efficiency or `% MA used` is defined as the pounds ofMA grafted into the polymer divided by the pounds of MA pumped into theextruder multiplied by 100.)

The amount of unreacted maleic anhydride remaining in the samples wasfound to be negligible by using a method based on extraction andhydrolysis. A 1 gram sample was heated with 10 ml of methylene chlorideand 10 ml. of water at 125° C. in a pressure vessel for 1 hour andcooled to room temperature. One ml of the clear, top aqueous layer wasthen diluted to 10 ml with water and analyzed for U. V. absorption at208 nm. A calibrated graph of absorbance vs. percent MA from knownsamples facilitated determination of `% free MA`, or the amount ofunreacted MA expressed as weight percent. Values ranged from 0.1 to 0.4wt-%.

Molecular weights were obtained by using a Waters 150° C. Gel PermeationChromatograph with three Waters HT columns (10,000; 100,000; and1,000,000 angstroms) at 140° C. The calibration standard waspolypropylene (Mw=108,000; Mn=32,500). Samples were dissolved ino-di-chlorobenzene at 140° C.

In order to calculate the moles of polypropylene for the ratio ofpolypropylene/peroxide (moles/moles) the weight of polypropylene wasdivided by 42, the molecular weight of propylene.

Example 1

Pellets of polypropylene from Eastman Chemical Company as TENITE P4-026with a melt flow rate of 1.2 were fed into the inlet hopper of a 90 mmtwin screw extruder having 13 consecutive equivalent barrels all at 200°C. at 150 rpm at a rate of 272 kg per hour. Molten maleic anhydride at90° C. was pumped into port 1 on barrel 1 adjacent to the inlet hopperat a rate of 10.9 kg per hour. LUPERSOL 101[2,5-dimethyl-2,5-bis-(t-butylperoxy)hexane] from Elf Atochem at 1.1 kgper hour was pumped into port 2 on barrel 2. A vacuum, 30 inches ofMercury, (760 mm) was pulled on port 8 and 10 located on barrels 8 and10. The pale yellow product was extruded as molten strands from barrel13, was solidified under water, and was then cut into pellets. Theproduct was analyzed with the following results: acid number=8.7; numberaverage molecular weight (Mn)=48,000; weight average molecular weight(Mw)=119,000; yellowness index color=51; and percent maleic anhydrideutilized=37% (37% efficiency).

Example 2

This example was carried out essentially as in Example 1 except that theRPM was changed to 292. The maleated polypropylene produced was analyzedwith the following results: acid number=10.1; Mn=43,000; Mw=105,000;yellowness index color=49; and maleic anhydride used=43% (43%efficiency).

Example 3

This example was carried out essentially as in Example 2 except that theamount of LUPERSOL 101 was changed to 2.4 kg per hour. The maleatedpolypropylene produced was analyzed with the following results: acidnumber=16.4; Mn=30,000; Mw=72,000; yellowness index color=48; and maleicanhydride used=70% (70% efficiency).

Example 4

This example was carried out essentially as in Example 3 except that theRPM was changed to 150. The maleated polypropylene produced was analyzedwith the following results: acid number=14.6; Mn=31,000; Mw=87,000;yellowness index color=56; and maleic anhydride used=62% (62%efficiency).

Example 5

This example was carried out essentially as in Example 4 except that theLUPERSOL 101 was changed to 0.5 kg per hour and the maleic anhydride waschanged to 4.5 kg per hour. The maleated polypropylene produced wasanalyzed with the following results: acid number=5.9; Mn=47,000;Mw=118,000; yellowness index color=25; and maleic anhydride used=60%(60% efficiency).

Example 6

This example was carried out essentially as in Example 5 except that theLUPERSOL 101 was changed to 1.1 kg per hour. The maleated polypropyleneproduced was analyzed with the following results: acid number=9.1;Mn=36,000; Mw=89,000; yellowness index color 24; and maleic anhydrideused=93% (93% efficiency).

Example 7

This example was conducted essentially as in Example 6 except that theRPM was changed to 292. The maleated polypropylene produced was analyzedwith the following results: acid number=4.8; Mn=51,000; Mw=130,000;yellowness index color=33; and maleic anhydride used=49% (49%efficiency).

Example 8

This example was carried out essentially as in Example 7 except that theLUPERSOL 101 was changed to 0.5 kg per hour. The maleated polypropyleneproduced was analyzed with the following results: acid number=3.0;Mn=57,000; Mw=148,000; yellowness color index 32; and maleic anhydrideused=31% (31% efficiency).

Example 9

This example was carried out essentially as in Example 8 except that theLUPERSOL 101 was changed to 0.3 kg per hour. The maleated polypropyleneproduced was analyzed with the following results: acid number=1.8,Mn=65,000, Mw=165,000, yellowness index color 33; and maleic anhydrideused=18% (18% efficiency).

Example 10

This example was carried our essentially as in Example 9 except that theRPM was changed to 150. The maleated polypropylene produced was analyzedwith the following results: acid number=3.5, Mn=58,000, Mw=145,000,yellowness index color=23; and maleic anhydride used=36% (36%efficiency).

Example 11

This example was carried out essentially as in Example 10 except thatthe maleic anhydride was changed to 10.9 kg per hour. The maleatedpolypropylene produced was analyzed with the following results: acidnumber=5.5, Mn=64,000, Mw=168,000, yellowness index color=36; and maleicanhydride used=23% (23% efficiency).

Example 12

This example was carried out essentially as in Example 11 except thatthe RPM was changed to 292. The maleated polypropylene produced wasanalyzed with the following results: acid number=3.6, Mn=60,000,Mw=150,000, yellowness index color=47; and maleic anhydride used=15%(15% efficiency).

Example 13

This example was carried out essentially as in Example 12 except thatthe LUPERSOL 101 was changed to 0.5 kg per hour. The maleatedpolypropylene produced was analyzed with the following results: acidnumber=6.0, Mn=63,000, Mw=135,000, yellowness index color=44; and maleicanhydride used=26% (26% efficiency).

Example 14

This example was carried out essentially as in Example 1 except that theRPM was changed to 200 and the maleic anhydride was changed to 16.3. Themaleated polypropylene produced was analyzed with the following results:acid number=5.4, Mn=60,000, Mw=143,000, yellowness index color=64; andmaleic anhydride used=15% (15% efficiency).

Example 15

This example was carried out essentially as in Example 14 except thatthe RPM was changed to 292. The maleated polypropylene produced wasanalyzed with the following results: acid number=4.2, Mn=71,000,Mw=190,000, yellowness index color=63; and maleic anhydride used=12%(12% efficiency).

Example 16

This example was carried out essentially as in Example 15 except thatthe maleic anhydride was 21.8 kg per hour. The maleated polypropyleneproduced was analyzed with the following results: acid number=3.7,Mn=68,000, Mw=192,000, yellowness index color=76; and maleic anhydrideused=8% (8% efficiency).

Example 17

This example was carried out essentially as in Example 16 except thatthe LUPERSOL 101 was changed to 4.5 kg per hour. The maleatedpolypropylene produced was analyzed with the following results: acidnumber=9.0, Mn=67,000, Mw=177,000, yellowness index color=75; and maleicanhydride used=19% (19% efficiency).

Example 18

This example was carried out essentially as in Example 17 except thatthe maleic anhydride was 16.3 kg per hour. The maleated polypropyleneproduced was analyzed with the following results: acid number=12.0,Mn=54,000, Mw=129,000, yellowness index color=70; and maleic anhydrideused=34% (34% efficiency).

Example 19

This example was carried out essentially as in Example 2 except that theLUPERSOL 101 was changed to 3.4 kg per hour. The maleated polypropyleneproduced was analyzed with the following results: acid number=16.9,Mn=34,000, Mw=82,000, yellowness index color=50; and maleic anhydrideused=72% (72% efficiency).

Example 20

This example was carried out essentially as in Example 15 except thatthe LUPERSOL 101 was changed to 0.5 kg per hour. The maleatedpolypropylene produced was analyzed with the following results: acidnumber=4.0, Mn=62,000, Mw=159,000, yellowness index color=58; and maleicanhydride used=11% (11% efficiency).

Example 21

This example was carried out essentially as in Example 9 except that themaleic anhydride was changed to 2.3 kg per hour. The maleatedpolypropylene produced was analyzed with the following results: acidnumber=2.4, Mn=65,000, Mw=152,000, yellowness index color=20; and maleicanhydride used=49% (49% efficiency).

Example 22

This example was carried out essentially as in Example 21 except thatthe RPM was changed to 150. The maleated polypropylene produced wasanalyzed with the following results: acid number=4.4, Mn=53,000,Mw=124,000, yellowness index color=23; and maleic anhydride used=90%(90% efficiency).

The above examples are summarized below in Table 1 along with the threeimportant ratios.

                                      TABLE 1                                     __________________________________________________________________________    Reagents           Product Properties                                                                        Reagent Ratios                                      Perox                                                                            MA kg MA                                                                             % MA                                                                              Acid                                                                             Mn,                                                                              Mw,                                                                              Index                                                                            PP/MA                                                                             PP/perox.                                                                          MA/perox                                #  RPM  kg/hr   kg/hr  Used    Used     #   k    k   Color     kg/kg                                                mole/mole    mole/mole                __________________________________________________________________________    1 150                                                                              1.1                                                                              10.9                                                                             4.0 37  8.7                                                                              48 119                                                                              51 25  829  14                                      2  292   1.1   10.9    4.7      43     10.1   43   105    49       25                                                    829         14                     3  292   2.4   10.9    7.6      70     16.4   30    72    48       25                                                    398          7                     4  150   2.4   10.9    6.7      62     14.6   31    87    56       25                                                    398          7                     5  150   0.5     4.5   2.7      60      5.9   47   118    25       60                                                   2072         15                     6  150   1.1     4.5   4.2      93      9.1   36    89    24       60                                                    829          6                     7  292   1.1     4.5   2.2      49      4.8   51   130    33       60                                                    829          6                     8  292   0.5     4.5   1.4      31      3.0   57   148    32       60                                                   2072         15                     9  292   0.3     4.5   0.8      18      1.8   65   165    33       60                                                   3452         25                     10 150   0.3     4.5   1.6      36      3.5   58   145    23       60                                                   3452         25                     11 150   0.3   10.9    2.5      23      5.5   64   168    36       25                                                   3452         60                     12 292   0.3   10.9    1.7      15      3.6   60   150    47       25                                                   3452         60                     13 292   0.5   10.9    2.8      26      6.0   63   135    44       25                                                   2072         34                     14 200   1.1   16.3    2.5      15      5.4   60   143    64       17                                                    829         22                     15 292   1.1   16.3    2.0      12      4.2   71   190    63       17                                                    829         29                     16 292   1.1   21.8    1.7       8      3.7   68   192    76       13                                                    829          7                     17 292   4.5   21.8    4.2      19      9.0   67   177    75       13                                                    207          5                     18 292   4.5   16.3    5.5      34     12.0   54   129    70       17                                                    207           5                    19 292   3.4   10.9    7.8      72     16.9   34    82    50       25                                                    276           5                    20 292   0.5   16.3    1.9      11      4.0   62   159    58       17                                                   2072          53                    21 292   0.3     2.3   1.1      49      2.4   65   152    20      120                                                   3452          13                    22 150   0.3     2.3   2.0      90      4.4   53   124    23      120                                                   3452          13                  __________________________________________________________________________

What is claimed is:
 1. A process for the production of maleatedpolypropylene comprising:(a) continuously forming an intimate mixture ofmolten polypropylene and molten maleic anhydride at one end of areactor, (b) continuously introducing a free radical initiator into saidintimate mixture of molten polypropylene and molten maleic anhydride toinitiate the grafting of the maleic anhydride onto the moltenpolypropylene to produce a maleated polypropylene, and (c) continuouslyremoving the maleated polypropylene product from the opposite end ofsaid reactor,wherein the weight ratio of polypropylene to maleicanhydride is about 10 to 200, the molar ratio of polypropylene to freeradical initiator is about 200 to 4,000, and the molar ratio of maleicanhydride to free radical initiator is about 1 to
 70. 2. The processaccording to claim 1 wherein the weight ratio of polypropylene to maleicanhydride is about 25 to
 60. 3. The process according to claim 1 whereinthe molar ratio of polypropylene to free radical initiator is about 270to 2,100.
 4. The process according to claim 1 wherein the molar ratio ofmaleic anhydride to free radical initiator is about 3.5 to
 15. 5. Theprocess according to claim 1 wherein the melt flow rate of saidpolypropylene in (a) is about 0.1 to 50 at 230° C.
 6. The processaccording to claim 5 wherein the melt flow rate of the polypropylene isabout 0.1 to 20 at 230° C.
 7. The process according to claim 1 whereinsaid reactor is a screw extruder.
 8. The process according to claim 1wherein said free radical initiator is a peroxide having a half lifegreater than 3 seconds at 180° C.
 9. The process according to claim 8wherein said peroxide is selected from the group consisting ofditertiary butyl peroxide, tertiary butyl hydroperoxide, cumenehydroperoxide, p-menthane peroxide, p-menthane hydroperoxide and2,5-dimethyl-2,5-bis-(t-butylperoxy)hexane.
 10. The process according toclaim 1 wherein step (b) is conducted at a temperature between 190 and205° C.
 11. The process according to claim 1 wherein the reactionproceeds at an efficiency rate of greater than 35 percent maleicanhydride incorporation into polypropylene.
 12. The process according toclaim 1 wherein the efficiency rate is at least 49 percent maleicanhydride incorporation into polypropylene.
 13. The process according toclaim 7 wherein said screw extruder is a twin screw extruder run at anRMP of 50 to 400 and the residence time of said molten polypropylene insaid reactor is about 0.45 to 2.5 minutes.